Several attempts have been made to produce aromatic aldehydes by hydrogenation of aromatic carboxylic acids, but one great problem common to all of these attempts has been that only a low yield is obtained if general-purpose hydrogenation catalysts are used. U.S. Pat. No. 4,328,373 reports that benzaldehyde can be formed by hydrogenation of benzoic acid in the presence of a zirconium oxide catalyst. However, according to experiments conducted by the present inventors, if zirconium oxide prepared by conventional techniques is used as a catalyst, the high temperature that is necessary for the reaction is detrimental to the yield of the end product and the life of the catalyst.